Basic Science Flashcards by Libby McMeekin

Describe the stages of HCl formation

CO2 from blood>H2CO3 (unstable carbonic acid)
H2CO3<> H2 + HCO3
H2 for H/K pump + HCO3/Cl pump (HCO3 out, HCl in)
HCl + H2O @basolateral membrane

How well did you know this?

Not at all

Perfectly

What controls ACh, gastrin and histamine secretion?

ACh=neurocrine
Gastrin=endocrine
Histamine=paracrine

How well did you know this?

Not at all

Perfectly

What stimulates acid secretion?

Sight
Smell
Taste
Thought of food

How well did you know this?

Not at all

Perfectly

3 phases of gastric acid secretion

Cephalic
-stopping eating=dec. vagal activity

Gastric phase

dec. phase (inc. HCl)= dec. gastrin
-ve feedback

Intestinal phase
-acid in duodenum> secretin release>dec. gastrin + dec. gastrin stim of parietal cells

Fat/CHO in duodenum > GIP release>gastrin and parietal HCl sec.

How well did you know this?

Not at all

Perfectly

Role of intrinsic factor in B12 absorption

B12 cannot cross the membrane as its a charged molecule with intrinsic factor
If there’s no IF then B12 will pass right through and lead to pernicious anemia
No B12=RBCs can’t mature

How well did you know this?

Not at all

Perfectly

Role of gastric secretions

Produced by surface epithelium cells and mucous neck cells
Cytoprotective role
-protects from mechanical injury
-neutral pH (HCO3)=projects against gastric acid corrosion and pepsin digestion

How well did you know this?

Not at all

Perfectly

Role of enterogasterones

Act collectively to prevent more acid build up in duodenum

inhib gastric secretion
reduce gastric emptying
- inhib mobility/ contract pyloric sphincter

How well did you know this?

Not at all

Perfectly

What’re the enterogastrones?

Secretin
CCK
GIP

How well did you know this?

Not at all

Perfectly

Pepsinogen secretion formation

Pepsinogen= the zymogen=secreted by chief cells
Low pH (< 3) converts it
Pepsinogen promotes more pepsin making
Pepsins inactivated at neutral pH

How well did you know this?

Not at all

Perfectly

What’re the 6 components of bile?

Bile acids 
Lecithin
Cholesterol
Bile pigments 
-bilirubin from haemoglobin
Toxic metals 
-detoxify by adding proteins 
Bicarb
-neutralisation of the acid chyme

How well did you know this?

Not at all

Perfectly

What is bilirubin?

The predominant bile pigment, extracted from blood by hepatocytes and secreted into bile=bile is yellow

How well did you know this?

Not at all

Perfectly

Why is urine yellow and faeces brown?

Reabsorbed bilirubin excreted in urine=yellow urine

Bilirubin modified by bacterial squash enzymes=brown faeces

How well did you know this?

Not at all

Perfectly

What’re bile acids synthesised from and where are they synthesised?

In liver from cholesterol

Before secretion bile acids are conjugated with glycine or taurine= increased solubility of bile salts

How well did you know this?

Not at all

Perfectly

What’re the 3 layers of the gallbladder wall?

Mucosa
-folded=ruggae=expansion
Muscularis
-smooth muscle=contraction 
Serosa
-connective tissue

How well did you know this?

Not at all

Perfectly

How does the gallbladder concentrate bile?

Absorbs the Na and H2O

How well did you know this?

Not at all

Perfectly

What effect does CCK have of on the sphincter of Oddi and what causes CCK release?

Fat in duodenum=CCK release
CCK=sphincter of Oddi relaxes, gallbladder contracts to squeeze out bile
Discharge of bile into duodenum=fat solubilisation

How well did you know this?

Not at all

Perfectly

Summarise the action of CCK

Fat/amino acids in duodenum=CCK release
CCK=decreases gastric emptying 
CCK=increases pancreatic enzyme secretion
Gallbladder contraction
DIGESTION

How well did you know this?

Not at all

Perfectly

Summary of actions of secretin

Acid in duodenum=secretin 
Decreases gastric acid 
Decreases gastric emptying 
Increases duodenal HCO3 secretion 
Increases pancreatic HCO3 secretion
Increases HCO3 secretion 
NEUTRALIZATION

How well did you know this?

Not at all

Perfectly

What’s the function of the duodenum, ileum and jejunum?

Duodenum=gastric acid neuralization, digestion and iron absorption
Jejunum=95% of nutrient absorption
Ileum=NaCl/H2O absorption=chyme dehydration

How well did you know this?

Not at all

Perfectly

What does a virus cell absorb?

NaCl
Monosaccharides 
Amino acids
Peptides 
Fats 
Vitamins 
Minerals 
Water

How well did you know this?

Not at all

Perfectly

What does a crypt cell secrete?

Water

How well did you know this?

Not at all

Perfectly

Where is intestinal fluid secreted from?

~1500ml/day from epithelial cells lining crypts of Lieberkuhn

How well did you know this?

Not at all

Perfectly

Why’s H2O secretion important for nutrient digestion?

Maintain contents in a lumenal state
Promotes mixing of nutrients
Aids nutrient presentation to absorbing surface
Dilated and washes away potentially injurious substances

How well did you know this?

Not at all

Perfectly

How are K, Na + 2x Cl transported?

Co transported using an electrical gradient

Where is the chloride channel located and what does the Cl do?

Apical membrane | Makes an osmotic gradient so water can passively move through the cell

What’re the events that lead to the Cl Chanel opening?

ATP>cAMP> phosphorylation of PKA>Cl channel opens

What is the purpose of segmentation?

Primary mechanism during digestion Contraction then relaxation of short segments Mixes contents with enzymes Chyme comes into contact with absorbing surface

How are segmentation contractions generated?

Pacemaker cells in longitudinal muscle Intestinal basic electrical rhythm (BER) produces oscillations in membrane= potential>threshold>AP>contraction AP determines strength of contraction BER decreases as you go down the pathway

What does parasympathetic, sympathetic and autonomic stimulation do to gut contraction?

Parasympathetic=vagus=increases Sympathetic=decreases Autonomic=no effect

What is the migrating motility complex?

Pattern of peristalsis from antrum to ileum | As one wave ends, another begins

What does the arrival of food mean for the MMC?

=stops MMC and initiation of segmentation

What does the MMC act to?

Move undigested food into the large intestine | Limit bacterial colonisation of small intestine

What hormone is involved in the initiation of the MMC?

Motilin

How is intestinal movement mediated?

Myenteric plexus

Describe the gastroileal reflex

Gastric emptying=increase in segmentation activity in ileum - opening of ileocaecal sphincter - entry of chyme into large intestine - distension of colon - reflex contraction of ileocaecal sphincter - -prevents backflux into small intestine

What’s the 2 muscular layers of the colon?

Circular layer= complete | Longitudinal layer=incomplete

Where is the muscularis externae thicker than in the rectum?

Anal canal

What’s the epithelium in the anal canal?

Simple columnar

How are chymes dehydrated?

Actively transports Na from lumen into blood>osmotic absorption of water>dehydration of chyme>solid faecal pellets

What is fermented by bacteria in the large intestine?

Short chain FA’s=energy source in ruminants | Vit K=blood clotting

Describe the mechanisms controlling defeacation

Wave of intense contraction towards rectum | Distension of rectal wall made by mass movements of faecal matter into rectum>defaecation reflex>urge to defaecate

What is the innervation of the defaecation reflex?

Parasympathetic via pelvic splanchnic nerves | No sympathetic

Transit time to mouth, oesophagus, stomach, small intestine and colon

``` Mouth=1 min Oesophagus= 4-8s Stomach=2-4hrs Small intestine=2-4hrs Colon=10hrs-several days ```

PH of mouth, stomach, small intestine and colon

Mouth=6.5-7.5 Stomach=1.5-4 Small intestine=7-8.5 Colon=5.5-6.5

In what conditions can a facultative anaerobes grow

Can grow with or without O2 but may not thrive

In which conditions can obligate grow?

Can’t survive in O2

Is gut microbiota higher or lower in western individuals?

Lower

Do fatty diets have more or less diversity?

Less

Jobs of bacterial diversity?

``` Metabolism of dietary components Produce essential metabolites Defence against: -competition -barrier function -PH inhibition -immune system priming Grow in fibre Can use host derived (endogenous) substrate for growth ```

Why should fibre be included in diets?

``` Contain phytochemicals, anti-oxidants and vitamins Increases bacterial fermentation: -more phytochemicals -maintain pH -increase commensal population -supply of short chain FAs ```

What’re the 3 main FAs and their functions?

Butyrate -epithelial growth and regreneration Propionate - gluconeogenesis in liver - satiety signalling Acetate - transported in pheripheral tissues - lipogenesis

Why’s re the products of/ presence of bacteria important for a healthy gut?

Barrier effect - large numbers prevent colonisation of ingested pathogens - inhibit overgrowth of pathogenic bacteria Active competition exclusion PH inhibition

What must the immune system be able to do?

Respond to foreign/pathogenic agents | Actively down-regulate immune responses to self proteins, dietary antigens and commensal microbiota

Functions of the SI with regards to digestion?

Breaking food down to its components Decontaminated dirty food Controlled hydrolysis to avoid fluid shifts Absorption against nutrients

What digests proteins in the SI?

Trypsin | Chromotrypsin

How is fat digested in the SI?

Pancreatic lipase - absorbs glycerol and free FAs - via lacteal and lymphatic system

How’re carbs digested in the SI?

Pancreatic amylase - breakdown to disaccharides - final digestion by brush border disaccharides

How does the SI achieve its barrier function?

``` Regulating what gets in and out Low bacterial populations It’s a toxic environment -digestive enzymes -bile salts -presence of IgA ```

How does is the barrier of the SI maintained?

Immune sampling Monitoring the presence of pathogens Translocation of bacteria Gut associated lymphoid tissue (GALT)